Paper Summary
Imaging with separated wavefields (SWIM) is an innovative depth-imaging technology that uses upgoing and downgoing wavefields at the surface to deliver high-resolution images of the subsurface. It takes advantage of the extended illumination provided by surface-multiple energy, and thus, it exploits data that the seismic industry historically has treated as unwanted noise. The fundamental concept behind SWIM is based on using each receiver as a virtual source, effectively expanding the surface coverage of the seismic experiment and enhancing the subsurface illumination, particularly for shallow reflectors. By effectively turning the streamer spread into a source (and receiver) array, the resulting equivalent survey has spatial sampling that is much improved and a richer distribution of offsets and azimuths. The improved spatial sampling enhances the angular illumination greatly at every image point. Therefore, SWIM produces densely sampled angle gathers that provide greater opportunities for velocity-model building and for improved interpretation of complex structures. Several issues need to be considered for proper imaging with SWIM: migration-imaging conditions, attenuation of cross talk, and acquisition design. The latter must be addressed to support proper sampling of both upgoing and downgoing wavefields used for imaging. A broad overview and examples of these subjects are presented. Applications to a deepwater wide-azimuth (WAZ) survey from the Gulf of Mexico and a shallow-water narrow-azimuth (NAZ) data set from offshore Malaysia demonstrate the enhanced areal illumination and improved imaging resolution from imaging using multiple-reflection energy.